Multi-Agent gatekeeper: Safe Flight Planning and Formation Control for Urban Air Mobility

2025-11-24

AI Summary

Addressing the lack of formal safety guarantees and dynamic adaptability for multi-vehicle formation flight in complex 3D urban air mobility (UAM) environments, this paper proposes a safety-critical cooperative framework based on a leader–follower architecture. The method integrates a precomputed backup trajectory set, an online formation tracking controller, and leader-path-dependent safe backup maneuvers—extending the Guardian algorithm to 3D multi-robot systems for the first time. All components are formally verified to ensure collision avoidance under bounded disturbances and actuation limits. The framework achieves provable safety without sacrificing real-time performance: in 100 randomized high-fidelity simulations, it attains 100% obstacle avoidance success, outperforming both Control Barrier Function (CBF) and Nonlinear Model Predictive Control (NMPC) baselines. Furthermore, experimental validation is conducted on a physical quadcopter swarm, confirming practical feasibility and robustness in real-world deployment.

Technology Category

• Intelligent Robots: Multi-Robot Systems
• Multiagent Systems: Multiagent Systems under Uncertainty
• Planning, Routing, and Scheduling: Replanning and Plan Repair

Application Category

• Responsible Web: Machine-in-the-loop, human agency and autonomy
• Security and Privacy: Large-scale security measurements
• Systems and Infrastructure for Web, Mobile and WoT: Applied ML and AI for Web-based mobile applications

Abstract

We present Multi-Agent gatekeeper, a framework that provides provable safety guarantees for leader-follower formation control in cluttered 3D environments. Existing methods face a trad-off: online planners and controllers lack formal safety guarantees, while offline planners lack adaptability to changes in the number of agents or desired formation. To address this gap, we propose a hybrid architecture where a single leader tracks a pre-computed, safe trajectory, which serves as a shared trajectory backup set for all follower agents. Followers execute a nominal formation-keeping tracking controller, and are guaranteed to remain safe by always possessing a known-safe backup maneuver along the leader's path. We formally prove this method ensures collision avoidance with both static obstacles and other agents. The primary contributions are: (1) the multi-agent gatekeeper algorithm, which extends our single-agent gatekeeper framework to multi-agent systems; (2) the trajectory backup set for provably safe inter-agent coordination for leader-follower formation control; and (3) the first application of the gatekeeper framework in a 3D environment. We demonstrate our approach in a simulated 3D urban environment, where it achieved a 100% collision-avoidance success rate across 100 randomized trials, significantly outperforming baseline CBF and NMPC methods. Finally, we demonstrate the physical feasibility of the resulting trajectories on a team of quadcopters.

Problem

• Ensuring collision avoidance in multi-agent formation flight
• Providing safety guarantees for 3D urban air mobility
• Addressing adaptability limitations in existing formation control methods

Innovation

• Hybrid architecture with leader tracking pre-computed trajectory
• Follower agents use backup maneuvers along leader path
• Formally proven collision avoidance in 3D environments